In a subsea wellhead system, an annulus seal assembly may seal the annulus between the wellhead housing and the OD of the casing hanger. This seal (or seal assembly) is conventionally run in with a running tool, which also runs and lands the casing hanger. The running tool may be manipulated so as to cause the seal to be set and then tested, typically from a pressure above to a pressure at or below the working pressure of the wellhead system.
Annulus seal assemblies have performed well in subsea wellhead systems at normal temperatures of 250 degrees F. or below. However, it has become desirable to have such seals perform at elevated temperature of 350 degrees F. or higher, i.e., during high temperature production operations. Such seals are difficult to design using normal elastomers for sealing integrity. Using an ‘all-metal’ design for the annulus seal assembly, the undesirable aspects of the elastomer are eliminated, such as thermal expansion properties, hydrostatic compression properties, high temperature degradation properties and degradation in the presence of drilling/production fluids. The all-metal properties are particularly needed during production operations (as compared to the drilling phase) where high temperatures might be present downhole for extended time periods.
The disadvantages of the prior art were overcome by the present invention, and an improved seal assembly for use in a subsea wellhead system is hereinafter disclosed.